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  • Title: Calcium-promoted catalytic degradation of PCDDs, PCDFs, and coplanar PCBs under a mild wet process.
    Author: Mitoma Y, Tasaka N, Takase M, Masuda T, Tashiro H, Egashira N, Oki T.
    Journal: Environ Sci Technol; 2006 Mar 15; 40(6):1849-54. PubMed ID: 16570607.
    Abstract:
    The authors achieved highly efficient degradation of polychlorinated aromatic compounds, including polychlorinated dibenzo-p-dioxins, dibenzofurans, and dioxin-like compounds such as coplanar polychlorinated biphenyls (co-PCBs), which are known as persistent organic pollutants. Degradation was accomplished in 24 h through a simple stirring operation using safe and high workability metallic calcium, which acts as both a scavenger and a reducing agent, and Rh/C catalyst in an alcohol solution under mild conditions in a sealed tube at 25 degrees C without a temperature increase within 0.15 MPa of increasing internal pressure during the reaction. In this system, reductive dechlorination by metallic calcium and catalytic reduction by Rh/C and generated hydrogen gas, without any external addition of hydrogen, exert a synergistic effect on the degradation of chlorinated compounds. Alcohol was used as a proton source and hydrogen, which was generated by a side reaction, causes an increase in the activity of Rh/C catalyst. Through the degradation of 4-chloroanisole in ethyl alcohol, anisole and cyclohexyl methyl ether were obtained in good conversions. Using ethyl alcohol as a solvent, treatment of dioxins and co-PCBs in a solution was markedly effective for degradation to reduce 2806 pg TEQ/ml of initial concentration to 31.8 pg TEQ/ml; its yield was 98.5%. Moreover, degradation in methyl alcohol took place in a 99.3% yield. That concentration ultimately reached 20.3 pg TEQ/ml under a mild wet process. All congeners of dioxins and co-PCBs were degraded in high conversions. In this degradation, lower aliphatic alcohol, such as methyl alcohol, is effective for making a new calcium surface as compared to alcohol with more methylene chains. In addition, it seemed that a higher pressure of hydrogen was easily generated in methyl alcohol, and then catalytic degradation was effectivley influenced.
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